SQL 2000 - Sum in a Group By

Working on an old SQL 2000 DB.
Having problem with a simple Select. Can someone give a quick hand

There are two number (Int) columns in the select. I need to group by 3 other fields. The number fields are being selected as SUM().
If I include the number fields in the Group By, I get too many rows as most of the values are different.
If I exclude them from the group, I get error: 'Not in aggregate function or Group by'. Why does it not recognize SUM as an aggregate?
is it the column type?

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